Subscribe!A recent piece from NPR, 'Smart Science Writing from a 'Physics Phobe'' highlights a work by Jennifer Ouellette, "Black Bodies and Quantum Cats". The title is a reference to black body radiation and Schroedinger's cat, but I won't go into detail about those. My issue here is that the her writing demonstrates only a superficial understanding of the science, basic high school level science at that.
In the piece, an excerpt is included. In this excerpt, she gives an interesting if brief history of roller coasters along with an anecdote about the maiden run of 'Apollo's Chariot' in Maryland. However, that's where the credibility ends. In attempting to explain the phenomenon involved she refers to potential and kinetic energies. She states that the roller coaster is "always shifting between potential (stored) and kinetic (released) energy". A body does not shift between types of energies. It can gain or lose the different types of energy, so it can be said that the body is having its total energy converted between the two types. We will igore energy losses due to friction.
The coaster train is initially pulled up the first hill, giving it more and more potential energy as it rises. The potential energy is a function of height and mass (PE=mgh, where m=mass, g=Earth gravitational constant, 9.8 m/s^2, and h=height). Once at the top of the first hill, the train has all the energy it will have for the duration of the ride. The total energy is a sum of potential and kinetic energies, E=KE+PE. At the top of the hill, KE=0, such that total energy, E, is equal to the potential energy. As it rolls down the hill, it begins losing potential energy and gaining kinetic energy. Kinetic energy is a function of mass and speed (KE=0.5*mv^2, v=speed). If the train goes all the way down such that its height is zero, all of the potential energy has been converted to kinetic energy and the train is traveling as fast as it possibly can travel. At h=0, PE=0 and E=KE. Once the train begins going up the next hill, it slows because kinetic energy is being lost and potential energy gained. The take home message is that if you know your height, you can always calculate your speed. The highest speed the train can travel is dependent upon the height of the first hill.
Roller coasters simply don't go up and down hills, though. The tracks twist and turn, causing the train and passengers to experience a range of forces pushing them around. These are sometimes mistakenly referred (as Ouellette did) to as "g-forces". A g-force is simply a convenient unit to measure the magnitude of the force experienced, with one unit of g-force being equal to that of the Earth pulling you toward it. In her description, she attempts to explain the difference between weight and mass. She is correct that weight is mass multiplied by the acceleration due to gravity. However, mass is not "how many atoms make up our body". Different atoms have different masses. For example, carbon is 12 times as massive as hydrogen. Mass is the amount of matter in a body. If you could count the number of atoms in your body, you still wouldn't know your mass without knowing the mass of the individual atoms. By counting the number of different types of atoms, you could then work out your mass.
This review wasn't meant to go into alot of detailed explanation, although there is a fair amount. Ultimately, I just wanted to state that the book by Jennifer Ouellette oversimplifies some concepts as wall as makes some statements that are only partially correct. If someone claims to have avoided science writing and physics in particular for 25 years, don't expect them to suddenly be able to offer lucid explanations. Based on the excerpt, I would not recommend this to anyone wishing to understand physics. Instead, look for something written by Richard Feynmann
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